This invention relates to a process for the preparation of an ester of cyanoacetic acid which is a valuable chemical intermediate, especially in the preparation of pesticides such as esters of 2-(2,2-dichlorovinyl)-cyclopropanecarboxylic acids, such as are disclosed in U.K. Pat. No. 1,413,491.
In a preferred embodiment of this invention 3-methyl-2-butenyl cyanoacetate, sometimes known as prenyl cyanoacetate (PCA): ##STR3## is produced. PCA is a valuable intermediate in the manufacture of ethyl 3,3-dimethyl-2-(2,2-dichlorovinyl)-cyclopropanecarboxylate (EDV) which is itself the acid half of the well-known synthetic insecticidally-active pyrethoid ester "cypermethrin" (alpha-cyano-3-phenoxybenzyl 3,3-dimethyl-2-(2,2-dichlorovinyl) cyclopropanecarboxylate as disclosed in U.K. Pat. No. 1,413,491.
PCA can be converted into EDV by means of the following steps:
(a) PCA is rearranged by reaction with sodium hydroxide, in accordance with the procedure of Belgium Pat. No. 847,534, to produce 2-cyano-3,3-dimethylpent-4-enoic acid (CDPA): ##STR4##
(b) CDPA is reacted with carbon tetrachloride, according to the procedure of Belgium Pat. No. 856,490, to produce 2-cyano-3,3-dimethyl-4,6,6,6 tetrachlorohexanoic acid (CDTA): ##STR5##
(c) CDTA is cyclized, dehydrohalogenated and decarboxylated in the presence of a base, according to the procedure of Belgium Pat. No. 855,691, to produce 3,3-dimethyl-2-(2,2-dichlorovinyl) cyclopropanenitrile (DCVN): ##STR6##
(d) DCVN is hydrolyzed in the presence of dilute mineral acid in ethanol to produce EDV.
Although PCA, as produced by the process of this invention, is a compound of particular importance, other cyanoacetic acid esters within the scope of this invention process similar utility as intermediates in the production of insecticically-active compounds.